One of my aims in developing the splinebeam function is to carry out non-linear analysis of reinforced concrete beams, allowing for the greatly reduced flexural stiffness of reinforced concrete sections after cracking of the concrete. To that end, I have added the facility to specify the section stiffness span by span. Later versions will allow for the stiffness of individual segments to be specified, or for a non-linear moment-curvature relationship to be used. Dowload SplineBeam2_1.zip

The standard cubic spline formulation is based on the curvature and slope of the spline being continuous at nodes. Since a step in the section stiffness will result in a step in the curvature, the curvature has been replaced by the bending moment, and the governing equation becomes: